Why Coral Reefs Are Bleaching Faster Than Ever

Coral reefs are known for their vibrant, rainbow-hued colors. They are vital to 25% of ocean life, even though they only make up less than 1% of the planet’s surface. They provide food and shelter for aquatic creatures, protect beaches from erosion, and play an important role in the marine ecosystem. But in recent years, coral reefs have been experiencing bleaching. In fact, they are currently suffering the worst bleaching event on record. This video, shared by NPR, shows a glimpse of the damage.

A whopping 84% of coral reefs worldwide were affected by bleaching during the latest event, which began more than two years ago. Bleaching occurs when coral loses its color and turns white because it no longer recognizes the zooxanthella as its symbiont. (Zooxanthellae are photosynthetic cells that live inside the coral and create its beautiful colors.)

What Causes Coral Bleaching?

Coral bleaching is caused by stress, according to the National Ocean Service. But this isn’t the kind of stress caused by an upcoming deadline or personal worries. In this case, stress refers to physical harm to the coral reef. These stressors include changes in temperature, light, or nutrient levels, which can cause the coral’s algae to leave. This type of stress is caused by a variety of factors, such as changes in ocean temperature (either too warm or too cold); runoff and pollution reaching coral near the shore; overexposure to sunlight (often due to high temperatures); and extreme low tides that expose coral to the air. When coral is bleached, only its white, skeleton-like inner structure remains, making it weaker and less likely to survive in the harsh ocean environment.

Stressors of the coral reef also include rising sea temperatures and CO2 levels, storms, earthquakes, and volcanic eruptions. The main factor, however, is ocean warming caused by climate change, per the Great Barrier Reef Foundation. A temperature increase of just one degree Celsius for four weeks can cause bleaching. According to Coral Guardian, the surface water temperature of the ocean has increased by an average of 0.5°C since 1860.

Other causes of bleaching include overfishing, which disrupts the delicate balance of the reef; fishing with dynamite or cyanide, which damages surrounding life; tourism pressures that lead to physical damage; pollution that encourages harmful algae growth; the trade of hard coral for aquariums; and coral diseases.

Can Coral Reefs Survive Bleaching?

Although coral reefs can survive the process, bleaching stresses them and makes them more fragile and vulnerable to starvation and disease, as they lose the protective benefits of their colorful algae. If ocean temperatures decrease and other conditions return to normal, the algae may return to the coral, allowing the reefs to gradually regain their color and health.

The World Meteorological Organization confirmed that 2024 was the Earth’s hottest year on record, a trend driven largely by the burning of fossil fuels. The International Coral Reef Initiative reports that the current bleaching event began in January 2023, and it is unclear when it will end.

Research since 1961 has shown that the average temperature of the global ocean has increased, with the ocean absorbing more than 80% of the heat added to the climate system. If current trends continue and climate action is not taken, up to 90% of coral reefs could become functionally degraded or disappear by 2050.

Mass Bleaching Events

There have been many mass bleaching events in recent years, including one of the worst in 2005 when the U.S. lost half of its coral reefs in the Caribbean. In April 2024, the National Oceanic and Atmospheric Administration announced that we are experiencing the fourth global coral bleaching event—and the second in the past decade.

“As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” Derek Manzello, Ph.D., NOAA CRW coordinator, said in a statement. “When these events are sufficiently severe or prolonged, they can cause coral mortality, which hurts the people who depend on the coral reefs for their livelihoods.”

Don’t Despair

If you want to help save coral reefs, there are many small actions you can take that add up, according to ICRI. These include conserving energy by using energy-saving lightbulbs, switching off lights and appliances when not in use, and washing your clothes in water that is 10 degrees colder. The organization also recommends avoiding single-use plastics, spreading awareness of the issue, conserving water, and reducing, reusing, and recycling to keep trash out of oceans and landfills.

It’s the least we can do to protect these beautiful and important parts of marine life.